Our investigations of the chemistry and structure of nucleic acids and related molecules have continued. Current studies and results include the following: Poly 2-amino-8-methyldeoxyadenylic has been prepared and its physical properties studied. The opposing effects of the two substituents on heteroduplex formation are interpreted in terms of their influence on conformational equilibria of the polymer. Marked contrast of these effects in the ribo and deoxy series has been observed. High salt concentrations convert poly (2NH2A-dBrU) and poly (d2NH2A-dIU) to a different conformation, reported in the literature to be a left-handed Z form. 2D NMR studies, however, have clearly shown that the high salt conformation is A and not Z. The above A reversible to B conversion was found to be temperature dependent. The enthalpy of the process and ion release per nucleotide were determined. Solid phase cyanoethylphosphoramidite methods were used to synthesize DNA oligomers containing restriction endonuclease recognition sites. These will be used for physical studies. A 2D NMR study of GAATTCGAATTC containing the Eco RI site has been carried out with G. Govil (TIFR, Bombay). Conformational details of the sugar pucker, glycosidic angle, and secondary structure have been obtained. Spectroscopic studies of the helix-forming nucleoside, isoguanosine, have led to proposal of a novel structure for the helix, at variance with those suggested in the literature.